In manufacturing metal oxide TFT, the carrier channel formed by metal oxide is easily damaged when wet etching metal to form source electrode and drain electrode. Conventionally it requires forming an etching stop on the carrier channel to protect the carrier channel from the wet etching. The provision of the etching stop not only increases the thickness of the TFT, but also increases the cost of the TFT.
Furthermore, following the increase of definition of the liquid crystal display (LCD), the TFT is made smaller and smaller which cause the current density in the TFT to be increased. The high current density in the TFT can generate hot-carrier effect. The hot-carrier effect is very harmful to electronic component, which may result in a malfunction of the TFT.